Identifying and authenticating tangible articles, particularly high-value items, as being genuine is an important function. The art of photography and, more recently, electro-optical image recording, has enabled comparisons between an original and a suspect object, as exemplified in U.S. Pat. No. 5,521,984, where a reflected light microscope is used to make an image of very fine detail of subjects such as paintings, sculptures, stamps, gemstones, or of an important document. Forgery of an original work, or of an anti-counterfeiting device that is associated with goods of generally similar appearance, is one driving force for the art of authentication systems.
Though biometric and fingerprint identification systems may supersede many token-based access-control systems, an agreement without a document or a physical device has little weight in law: documents and devices are likely to persist as bonds of valid registration, allowance or entitlement, for example.
Rates of ‘false-accepts’ and ‘false-rejects’ are important for the utility of an authentication system, and closely related to the value of the entity or situation being controlled or to the security level required. A high ‘false-reject’ rate will lose consumer-confidence in the system, affecting both parties. A high-security facility or a passport-control may generally tolerate higher ‘false-rejects’ to the inconvenience of some person, with no ‘false-accepts.’ Similarly, for very high value items both rates should be close to zero. The examination and comparison processes can be precise and accurate, as exemplified in the U.S. Pat. No. 5,521,984 previously referred to, leaving overall security weakness in identification in the domain of the data-handling and storing processes employed.
The field of anti-counterfeiting devices for mid-price consumer goods and credit-cards has led to many inventions for two-dimensional devices for that market, including stamped transmission holograms and various improved diffractive optical devices. The utility of reflection holograms has some difficulties in cost and suitable materials: all holograms have limitations in scaling the subject matter. Some of these devices may be optically duplicated, however, and most have master dies that could be duplicated or misappropriated. In many cases these devices are read, the data is ‘digested’ and then compared to accompanying data. Abrasion-wear or flexing damage can cause problems with reading the authentic device and lead to higher ‘false-rejects.’ False-rejects' often require intervention by a human-being.
Some methods for device and document authentication use reflected coherent light as a method of obtaining a characteristic signature of the subject, as exemplified in U.S. Pat. No. 7,812,935. Generally, methods using speckle, complex diffractions or refraction have to contend with minor changes, unconnected with any fraud, causing large alterations in presented properties when read. The minor changes could occur at all points in the subject, e.g. thermal expansion, stress-fracturing, scratches or colour-fading; this creates difficulties in establishing identity without using multiple application of statistical percentiles to develop pass criteria, or may require data-digests to be made from encoding schemes held within the reading device.
The use of a third dimension, usually depth, in a security device is exemplified in U.S. Pat. No. 4,825,801, where glitter and dye-balls in a hardened resin, as a seal, practically defies successful duplication. This latter example's high-security application permits adequate time for the examination process. Subsequently, various multiple objects have been set in ‘hardenable’ liquids: by example, U.S. Pat. No. 7,353,994. Qualitatively these seem to be strong devices; quantifying the spatial features in them however, in a reading device, can be problematic.
Creating unique arrangements in a relatively thin security device is described in U.S. Pat. No. 7,793,837, wherein a captive brittle later in a consumer-card, such as a credit card, is intentionally shattered and the pattern of shards examined for authenticity.
In summary, these techniques have drawbacks including: physical changes to the token resulting in authentication failure; difficulties with reliability and implementing automated reading; and high costs.
Therefore, there is required a method and apparatus that overcomes these problems.